As a sensor used in detecting the shift ranges of an automatic transmission (hereinafter abbreviated as “AT”) for motor vehicles, there is conventionally known a stroke sensor that detects shift ranges by detecting the positions of a manual valve of an AT. The manual valve has a function of switching oil passages in conjunction with the shift ranges of the AT either inside in the oil) or outside the AT.
As the stroke sensor of this kind, there is known a contact-type stroke sensor in which the contact state of mechanical contact points is changed in conjunction with the linear reciprocating movement of a manual valve. In the contact-type stroke sensor, the mechanical contact points are often worn due to the sliding movement thereof.
In view of this, there is proposed a noncontact-type stroke sensor in which the operation of a manual valve is detected by providing a permanent magnet in the manual valve and detecting the position of the permanent magnet with a magnet sensing element. In the stroke sensor employing the permanent magnet, however, the shift range detection accuracy may possibly be reduced due to the demagnetization of the permanent magnet or the adsorption of metallic debris or the like existing in the oil within an AT.
In the meantime, the applicant of the subject case has proposed a stroke sensor (switch device) in which a plurality of sensor coils is arranged side by side in the axial direction of a manual valve (metal shaft) to detect shift ranges using the outputs of the sensor coils (see, e.g., Patent Document 1). In the stroke sensor disclosed in Patent Document 1, each of sensor coils creates a high frequency magnetic field and detects a metal (manual valve) adjacent thereto so that the stroke sensor detects a position of the manual valve in the linear reciprocating direction (i.e., the axial direction).
Patent Document 1: Japanese Patent Application Publication No. 2000-161475
In the stroke sensor disclosed in Patent Document 1, the sensor coils are arranged along the moving direction of the manual valve. Therefore, the shift ranges adjoining to each other differ from each other only in the output of one of the sensor coils. For that reason, if one of the sensor coils gets out of order, the outputs in the adjoining shift ranges become equal to each other. As a result, a wrong shift range may possibly be detected in error.